Dielectric anomaly and magnetic response of epitaxial orthorhombic YMnO 3 thin films
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V. Skumryev Institut Català de Recerca i Estudis Avançats (ICREA), Barcelona, Spain; and Departament de Física, Universitat Autònoma de Barcelona, Bellaterra 08193, Spain
V. Laukhin Institut de Ciència de Materials de Barcelona, Consejo Superior de Investigaciones Cientificas (CSIC), Campus UAB, Bellaterra 08193, Spain; and Institut Català de Recerca i Estudis Avançats (ICREA), Barcelona, Spain
F. Sánchez Institut de Cie`ncia de Materials de Barcelona, Consejo Superior de Investigaciones Cientificas (CSIC), Campus UAB, Bellaterra 08193, Spain
M.V. García-Cuenca, C. Ferrater, and M. Varela Departament de Física Aplicada I Óptica, Universitat de Barcelona, Diagonal 647, Barcelona 08028, Spain
J. Fontcuberta Institut de Ciència de Materials de Barcelona Consejo Superior de Investigaciones Cientificas (CSIC), Campus UAB, Bellaterra 08193, Spain (Received 26 December 2006; accepted 21 March 2007)
The structure, magnetic response, and dielectric response of the grown epitaxial thin films of the orthorhombic phase of YMnO3 oxide on Nb:SrTiO3 (001) substrates have been measured. We have found that a substrate-induced strain produces an in-plane compression of the YMnO3 unit cell. The magnetization versus temperature curves display a significant zero-field cooling (ZFC)-field cooling hysteresis below the Néel temperature (TN ≈ 45 K). The dielectric constant increases gradually (up to 26%) below the TN and mimics the ZFC magnetization curve. We argue that these effects could be a manifestation of magnetoelectric coupling in YMnO3 thin films and that the magnetic structure of YMnO3 can be controlled by substrate selection and/or growth conditions. I. INTRODUCTION
Understanding and tailoring coupling between the magnetic and dielectric properties of oxides is a very active field of research. The ultimate goal, to control the magnetic (dielectric) state by using an electric (magnetic) field, requires that both physical properties are coupled. Manganese oxides AMnO3, where A is a suitable rare earth, present a hexagonal or perovskite (orthorhombic) structure, depending on the size of the rare-earth cation; for the smaller rare earths (Ho–Lu, Y), the hexagonal phase (in bulk) is the equilibrium phase, whereas the orthorhombic phase is obtained for the larger rare earth (Tb, Dy, and Gd). Of relevance here is that, whereas at low temperature both families of compounds display an antiferromagnetic (AF) order, the ferroelectric (FE) order sets in at temperatures [i.e., FE Curie temperature (TCFE)] a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2007.0264 2096 J. Mater. Res., Vol. 22, No. 8, Aug 2007 http://journals.cambridge.org Downloaded: 14 Mar 2015
much above the AF Néel temperature (TN) in the hexagonal structure, but it occurs at temperatures below the TN in materials with orthorhombic structures. For instance: for the hexagonal YMnO3, TCFE is ∼900 K and TN is ∼80 K,1,2 and for the orthorhombic TbMnO3, TCFE is ∼30 K and TN is ∼40 K.3 The magnetism and ferroelectricity usually ex
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